Polarized layer in copper-oxide photovoltaic cell



Oct. 12, 1937. E. D. WILSON 2,095,782

POLARIZED LAYER IN COPPER OXIDE PHOTOVOLTAIG CELL Original Filed May 8, 1935 l4 7Fans nqrent I4 [5 l5 profechve caafmy,

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Copper oxide Copper:

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WITNESSES: INVENTOR q m Earl D. Wilson.

ATTORN Patented Oct. 12, 1937 PATENT OFFICE POLARIZED LAYER IN COPPER-OXIDE PHOTOVOLTAIG CELL Earl D: Wilson, Wilkinsburg, Pa., assignor to Westinghouse Electric A; Manufacturing Comliany, East Pittsburgh, Pa a corporation oi.

Pennsylvania Application May 8, 1935. Serial No. 20.362 Renewed March 17, 1987 7 Claims.

This application is a continuation in part of my copending applications Serial No. 578,399, filed December 1, 1931, and Serial No. 4,285, filed January 31, 1935.

My invention relates to photo-sensitive devices and it has particular relation to photo-sensitive devices of the dry photo-voltaic type.

In the prior art, photo-sensitive devices have been constructed of a translucent film of cuprous l oxide upon copper. Contact has been made to the oxide and to the copper by mechanical pressure or other equivalent means. Light passing through the copperoxide caused the electrons to pass across the juncture between the oxide and 1 the copper. While such a cell was responsive to light, yet its sensitivity was not of a very' high order. It was found thatthe sensitivity of such a cell was limited to the red portion of the visible spectrum, namely, the range from about 850 go millimicrons to 700 millimicrons, and that the cell was not sensitive to green light, which has a position in the visible spectrum to which the human eye is most sensitive. Such a device, furthermore, had to be very carefully manufactured and assembled in view of the necessarily thin delicate coating of transparent copper oxide.

It is an object of my invention to utilize the photo-electric properties of copper oxide, but to avoid all of the above-mentioned difliculties of so the copper-copper oxide cell just described.

It is another object of my invention to provide a photo-sensitive device having a copper oxide layer upon a copper base, and to provide the electron discharge device from the copper oxide to 36 another metal instead of to the copper, as in the prior art devices.

Another object of my invention is to provide such a photo-sensitive device that has its maximum relative response in the central portion of the visible spectrum.

More specifically stated, it is an object of my invention to form a photo-sensitive device by oxidizing copper, and forming a layer of polarized gas on the copper oxide covered with a layer of translucent metal whereby the copper oxide and metal are electrodes bounding a discharge path across the polarized layer of gas.

Other objects of my invention will become evident from the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure 1 is a schematic view with parts of the photo-sensitive device in cross-section and a meter in elevation;

Fig. 2 is an enlarged view in cross-section of the extreme right-hand portion of the photosensitive device of Fig. 1; I

Fig. 3 is a cross-section view with someparts in elevation of a preferred type of apparatus for forming the layer of polarized gas and translucent metal film on the copper oxide;

Fig. 4 is an enlarged view in cross-section with some parts in elevation of the copper-copper oxide disc carrying member of Fig. 3; and

Fig. 5 is a curve showing the relative spectrum response of my photo-sensitive device manufactured under the trade name Photox with the range of visibility of human eyes. I The completed preferred form of my photosensitive device is disclosed in Fig. 1 with a portion at the extreme right enlarged in detail in Fig. 2. As disclosed in these figures, the form of this photo-sensitive device is preferably that of a disc in which the base is a thick disc of copper Ill. 1 Upon this layer of copper is a layer of copper oxide ll, preferably of a thickness to be opaque to prevent any light passing through to the copper and also of a thickness 'to withstand rough treatment without cracking through to the copper. On the surface of the copper oxide is a layer of polarized gas l2. This layer of polarized gas is very much enlarged and out of proportion for the sake of illustration. Upon this polarized gas is a'translucent metallic film l3. This film can be of any suitable conducting material, but I prefer one of the noble metals and especially either gold or silver. Upon the central portion of the translucent film, I prefer to place a transparent protective coating i4 and also to provide a ring 01' conducting material 15 to make contact with the gold film.

The cell as I have described it and as disclosed in these two figures is a generator of electricity in response to light passing through the translucent film and polarized gas to the oxide. A meter IS with its negative lead ll connected to the contact member l5 and its positive lead I8 connected to the copper will register a varying amount depending upon the intensity of iilumination of the light.

A preferred type of apparatus for performing the electron discharge elements of my photosensitive device is disclosed in Fig. 3. A disc of copper is oxidized at a temperature preferably of the order of 1000 0., and has formed upon its surface a thick layer of cuprous oxide. The disc is then preferably vacuum treated at 800 0., and then the oxide surface is cleaned with acid, preferably nitric acid. Any of the black cupric oxide is, of course, removed in this process, and the copper disc l0 has the red layer of cuprous oxide upon one surface. This disc is then placed within the container 20, preferably of a somewhat bell-shaped design, and having a ground glass fit 2| with a suitable base 22.- The atmosphere of the container 20 can be removed or changed or varied through a suitable outlet 23 connected to a pump. In the upper portion of the container is a holder 24 for the disc, and this container is suspended from a suitable support 25 having an electrical connection 26 passing through the container wall at 21.

The holder 24 is more clearly disclosed in Fig. 4 and preferably consists of a cylindrical container with a slight inturned rim 30 on its underside for holding the edge of the copper-copper oxide disc. The disc is placed with the oxide surface ll facing downward. A connection 3| makes contact between the back of the copper and the connection 26 passing to the exterior of the container 20.

In the bottom of the container is an electrode 32 with a lead 33 passing through the base to the exterior. Two connections 34 and 35 also preferably extend through the base to a position just below the holder 24 and have any suitable wire supporting means 36 upon their upper ends. A wire, preferably in the form of a coiled filament, 31 is supported by these supports 36 and secured thereto as by the screws 38. The filament 3'! is of suitable resistance and material to produce the electric current passing therethrough. On this wire is placed a material 39, of which the translucent or transparent film I3 is to be composed. This, as previously mentioned, is preferably of gold or silver.

The chamber within the container 20 is evacuated and then filled to about 30 microns of pressure with any suitable gas such as argon or air. If air is used, the pressure is merely reduced to this amount. A discharge is then passed from the electrode 32 to the disc with the disc negative. The electrons within the gas in the container will travel towards the electrode 32 and will collide with atoms of the gas, and the collision will create positively charged ions as well as other electrons. These ions of gas will "travel to the surface of the copper oxide II and impinge thereon and create a polarized layer of gas over the surface. This layer of polarized gas may be of the order of one or a few atoms thick. Nevertheless, I believe that this polarized gas with its positive charge will place the electrons in the copper oxide under tension. I believe that the orbits of the polarized gas and the electrons just within the surface or on the surface of the copper oxide are interlinked, so that while the tension is not sufficient to pull the electrons out of the copper oxide, yet the tension is sufficient to materially reduce the amount of work necessary to actually pull the electrons out of the copper oxide surface.

An atom or molecule of gas is said to be polarized when the electronic orbits are so perturbed that an effective electrical dipole results. Two charges of opposite sign separated by a finite distance constitute an electric dipole.

After the discharge between the electrode 32 and the disc has formed a polarized layer of gas on the copper oxide, the chamber is again evacuated and a current passed through the conductors 34 and 35 heating up the silver or gold 39 on the filament 31 and evacuating it upon the surface of the copper oxide and polarized layer of gas. The amount of evaporation is controlled so that this layer is merely a translucent film or even may be thin enough to be practically transparent. The cell is then removed and I preferably add the transparent protected coatings l4 and the contact rim IS on the surface of the translucent gold or silver film. The resulting cell is capable of delivering more than 10 microwatts per square inch at an illumination of 50 footcandles from an ordinary incandescent lamp.

One of the great advantages of my photo-sensitive device, which is known under the trade name Photox, is that it has a relative spectrum response comparable to that of the human eye. This feature is graphically illustrated in Fig. 5 showing the maximum response of the Photox in the green portion of the visible spectrum. The dotted lines in Fig. 5 represent the spectrum range of visibility curves for human eyes.

While I have described the polarized gas layer and the translucent film as being deposited upon the copper oxide surface in separate steps, yet it is possible to produce the polarized gas and metal film by a simultaneous discharge and transfer of material. The discharge, in such case, has to be strong enough to insure a sufilcient layer of polarized gas, as otherwise the cell will not be sensitive.

I desire to emphasize that the discharge provides the conductive medium for the gold or silver films to act as electrodes in receiving the ions from the copper oxide. The polarized gas, as previously explained, places the electrons in the copper oxide under a tension. The light energy passing through the translucent film l3 strikes the copper oxide and provides the additional energy necessary to haul these electrons out of the copper oxide and across the gas to the translucent film. This light energy accordingly generates a current that will pass through the conductors l1 and I8 and register on the microammeter l6.

If the layer I3 is placed upon the copper oxide layer ll without a prior glow discharge or a simultaneous glow discharge, then there will be no appreciable electron discharge from the copper oxide to this translucent film. This is true with the cells of the prior art. As previously pointed out, these cells depend upon the light striking the junction between the copper oxide II and the copper Ill so that the discharge device takes place from the copper oxide to the copper, and the direction of current is reversed from that of my device.

While I have used the term gas throughout yet this term is to include vapors such as water vapors, alcohol, acetane which I have found to be effective. Numerous other vapors may be used especially those having a high vapor pressure at room temperature which are obviously more convenient to use.

I also contemplate using polarized solid insulators or semi-conductors for the polarized layer. The substances would include waxes, resins, oils, sulphur and poorly conducting metallic oxides and compounds.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible, such as the shape, arrangement and materials of the elements of both the photo-sensitive device and the apparatus for constructing it. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art.

-I claim as my invention:

1. The method of forming a photo-sensitive device which comprises oxidizing copper, bomharding the surface of the oxidized copper. with positive gaseous ions and depositing a layer of a metal which is substantially inert photo-electrically and which is thin enough to be translucent on said oxide.

2. The method of forming a photo-sensitive device which comprises oxidizing copper, exposing said copper oxide to a glow discharge to form a polarized gas layer thereon, and evaporating a layer of a noble metal thin enough to be translucent on said polarized layer.

3. The method of forming a photo-sensitive device which comprises oxidizing copper, placing the oxidized copper in a container with a gaseous medium, passing a discharge through the gaseous medium with the copper oxide as a cathode surface to form a polarized layer of gas thereon, and evaporating a metal which is substantially inert photo-electrically and depositing a thin film of said metal on said polarized layer and oxide.

4. A light-sensitive device comprising copper, a layer of copper oxide on said copper, a polarized layer of gas on said oxide and a layer of conductive metal which is substantially inert photoelectrically on said gas and oxide, said oxide and conductive metal being electrodes bounding a discharge path across said polarized layer 01' gas made conductive by light.

5. A light-sensitive device comprising copper, a layer of copper oxide on said copper, a polarized layer of gas on said oxide and a layer of conductive material on said oxide and said polarized gas, said oxide and said conductive material being electrodes bounding a discharge path across said polarized layer made conductive by light,

said conductive material being the negative electrode and said oxide the positive electrode.

6. The method of forming a photo-sensitive device which comprises oxidizing copper, cleaning the oxidized copper with acid, bombarding the surface of the. oxidized copper with positive gaseous ions and depositing a layer of metal which is substantially inert photo-electrically and which is thin enough to be translucent on said oxide.

7. The method of forming a photosensitive device which comprises oxidizing copper, heat treating said oxidized copper in a vacuum, bombarding the surface of the oxidized copper with positive gaseous ions and depositing a layer of metal which is substantially inert photo-electrically and which is thin enough to be translucent on said oxide.

EARL D. WILSON. 

